Now that Dark-Alex has unlocked 480x272 resolution on the PSP,s native player, theres really no need for the likes of PMPMODAVC or PSPlayerMT.
Some would say that running PMP,s reduces battery comsumption (which it does) but on saying that its great to be able to run 480x272 true (as it where) PSP movies.
I think (but am not sure) that with the release of PS3 we are able to stream the movies to it and watch on your telly.
To play your XviD,s try PMPMOD or said mentioned PSPlayerMT.